Positive photoresists using an alkali-soluble resin and a photosensitizer such as a 1,2-naphthoquinone diazide compound or the like are known as resists used for manufacturing semiconductors such as IC, LSI, and the like and manufacturing display devices such as LCD and the like, and manufacturing printing original plates. There is proposed a positive photoresist composition using, as the alkali-soluble resin, a mixture containing a m-cresol novolac resin and p-cresol novolac resin as the alkali-soluble resin (for example, refer to Patent Literature 1).
The positive photoresist composition described in Patent Literature 1 is developed for the purpose of improving developability such as sensitivity and the like. However, recent increasing integration of semiconductors has brought about a tendency toward finer pattern lines and a demand for more excellent sensitivity, and the positive photoresist composition described in Patent Literature 1 has the problem that satisfactory sensitivity coping with finer lines cannot be achieved. Further, various heat treatments are performed in a process for manufacturing a semiconductor or the like, and thus a coating film of the positive photoresist composition is required to have high heat resistance. However, the positive photoresist composition described in Patent Literature 1 has the problem of unsatisfactory heat resistance.
Also, there is proposed, as a phenol resin having excellent resistivity and high heat resistance, a phenol resin for photoresist which is produced by reacting phenol such as m-cresol, p-cresol, or 2,3-xylenol with an aromatic aldehyde and then adding aldehyde (B) to the resultant reaction product and reacting both under an acid catalyst (for example, refer to Patent Literature 2). The phenol resin for photoresist has improved sensitivity as compared with usual ones but cannot satisfactorily cope with a recent high requirement level of heat resistance.
On the other hand, the photosensitivity of a novolac resin which is an alkali-soluble resin can be enhanced by improving alkali solubility. However, improvement in alkali solubility tends to decrease heat resistance, and improvement in heat resistance has the problem of decreasing photosensitivity. Therefore, it is difficult to satisfy high levels of both sensitivity and heat resistance of a novolac resin. There is proposed, as a resin increased in both sensitivity and heat resistance, a novolac phenol resin for photoresist using as a raw material a phenolic trinuclear compound produced by condensation of xylenol with a phenolic hydroxyl group-containing aromatic aldehyde (for example, refer to Patent Literatures 3 and 4).